It is important to assess the quality of newly constructed pavements and existing pavements. Quality issues include grade and roughness, crossfall and rutting, and cracking, spalling and faulting, and strength. The assessment of these quality issues typically involve pavement profile measurement. Manual methods of measuring profiles include typical surveying techniques, the Static Level Method as described in ASTM Standard Test Method E 1364-90 and the use of a Dip Stick as described in U.S. Pat. No. 4,473,960. Rutting and crossfall have been measured from vehicles with three to twelve single point acoustic or triangulation optical elevation sensors mounted along a transverse beam. An example of such a device is Highway products ARAN system. Roughness is measured at walking speeds with devices called profilographs which use a contact sensing wheel per ASTM Standard Test Method E 1274-88 and at highway speeds with inertial profilometers as described in U.S. Pat. No. 4741,207 and reference beam profilometers as described in UK TRRL Report 922. Surface deterioration has been determined by visual inspections and by photography and video taping. Strength is generally derived from deflection under a falling weight load using methods such as that described in ASTM Standard Test Method D 4964-87.
Efforts to measure deflection under a rolling wheel load include the use of dual transverse beams with elevation sensors such as described in U.S. Pat. No. 4,781,058 and an extension of the TRRL beam as in U.S. Pat. No. 4,571,695.
One effort at profile measurement has employed a rotating polygon and a modulated laser beam to illuminate and measure pavement cracking is described in U.S. Pat No. 4,796,998. The only effort known to Applicant to attempt to apply rotating polygon scanning with amplitude modulation and phase measurement for transverse profiling is described in SHRP-IDEA Project 006 Report. The method there described utilized a balanced mixer as a phase detector.
Techniques for determining the profiles of a surfaces by measuring the round trip time for a laser beam to travel to the surface and back is known. One such system is described by Cameron in U.S. Pat. No. 5,006,721. In U.S. Pat. No. 4,569,078, David Zuk describes a sensor using this concept to obtain an "image" of the surface of a target.
All of the above devices for measuring quality of pavement surfaces either collect the data at low highway speeds or do not provide enough detail for complete evaluation of the surface. What is needed is a device to provide detailed description of the profile of a pavement surface at speeds of as high as 50 miles per hour or higher.